Electroless deposition of a metal on plastics requires the preparation of the plastic surface to accept the electroless metal coating. Depending upon the type of plastic to be treated by electroless deposition, the prior art teaches numerous methods of surface treatment.
Electron sputtering or glow discharge surface treatments of polyvinyl chloride (PVC) plastics prior to electroless deposition improve the adherence of a subsequently deposited metal coating to the PVC substrate. However, these treatments require expensive vacuum equipment and are more labor intensive than a completely wet-chemical process.
Acid etchants such as phosphoric acids, sulfuric acid, chromic acid, and hydrochloric acid, roughen the surface of the plastic sufficiently to permit the deposition of adherent metal layers. However, the acid etchants tend to pit and degrade the surface of PVC plastic and are thus not suitable when a non-grainy conformal metal coating must be deposited.
High temperatures and high concentration of bases will also tend to etch or render PVC plastics porous. The porosity of the plastic presents many problems to workers skilled in the art desiring to apply a non-grainy conformal metal layer to the plastic by electroless deposition.
Thus, a chemical process which can pretreat a PVC plastic, without etching or degradation, to accept an adherent, non-grainy conformal metal layer by electroless deposition would be highly desirable.